This invention pertains to a process for the preparation of bishydroxy aromatic compounds.
Bishydroxy aromatic compounds, such as 9,9-bis(4-hydroxyphenyl)fluorene and 2,2-bis(4-hydroxyphenyl)propane (bisphenol-A), are useful monomers for preparing polycarbonates, polyesters and polyethers.
P. W. Morgan discloses in Macromolecules, 3, 536 (1971) the acid-catalyzed phenolation of aromatic and alkaryl ketones to bishydroxy aromatic compounds. For example, it is taught that fluorenone reacts with molten phenol in the presence of 3-mercaptopropionic acid and gaseous hydrochloric acid to yield 9,9-bis(4-hydroxyphenyl)fluorene.
U.S. Pat. No. 4,467,122 discloses the phenolation of aromatic ketones to bishydroxy aromatic compounds in the presence of gaseous hydrogen halide and at least one divalent, trivalent or tetravalent metal halide wherein the metal is selected from Groups IIA, IIB, IIIA, IVA, IVB, and VIIIB of the Periodic Table. For example, fluorenone is reacted with phenol in the presence of zinc chloride and gaseous hydrogen chloride to yield 9,9-bis(4-hydroxyphenyl)fluorene.
One disadvantage of the aforementioned processes is that hydrochloric acid and metal halides are corrosive to the metal equipment used in an industrial-scale process.
U.S. Pat. No. 4,675,458 teaches the phenolation of fluorenone to 9,9-bis(4-hydroxyphenyl)fluorene in the presence of sulfuric acid and a thiol promoter. Disadvantageously, the concentration of the sulfuric acid must be greater than 75 weight percent, preferably 85 to 100 percent, and the acid must be neutralized on work-up resulting in a waste problem. As a further disadvantage, the operating temperature must be maintained between about 20.degree. C. and 70.degree. C. to minimize sulfonated byproducts, thus requiring long reaction times.
More recently, U.S. Pat. No. 4,931,594 discloses the condensation of diaryl ketones, such as fluorenone, with phenols in the presence of acidic cation exchange resins to form aromatic bisphenol compounds. The ion exchange resins which are suitable are taught to include macroporous sulfonated crosslinked polystyrenes and the corresponding styrene/acrylate copolymers, or poly(perfluoroalkylene)sulfonic acid. Disadvantageously, the process requires high temperatures and the yield of the desired 4,4'-isomer of 9,9-bis(hydroxyphenyl)fluorene, is only 60 to 75 mole percent.
In view of the above, it is clear that a need exits to find a process for preparing bishydroxy aromatic compounds in high selectivity and yield of the desired isomer and without corrosion and waste problems.